Anthropic's Claude Designs Quantum Circuits That Beat the Best Published Ones

Anthropic said on October 16, 2026 that its Claude Mythos 5 model designed quantum circuits that improve on the best published designs, in some cases by an order of magnitude or more. The work was led by Andi Gu through Anthropic’s STEM Fellows Program, with mentorship from Anthropic quantum physicist Alek Kemeny, in collaboration with Susanne Yelin and Mikhail Lukin of Harvard University. The full paper, Discovering state-of-the-art quantum circuits with large language models, is posted on arXiv.

How the setup worked

The researchers gave Claude plain-language specifications for eight circuit tasks drawn from chemistry, optimization, quantum simulation, number theory and numerical computing. An independent evaluator program checked every candidate for correctness and scored it by its Toffoli gate count multiplied by its peak qubit count, a stand-in for how long and how big the computation would be. Claude worked in a closed loop: write a circuit design as Python code, receive the evaluator’s verdict and score, and revise, with no human input between rounds. The search started from a blank program and used the open-source OpenEvolve framework.

What it found

According to the paper, in seven of the eight tasks the discovered circuits significantly reduced both Toffoli and qubit counts relative to the state of the art. On the tasks with a published baseline, the combined gate-times-qubit cost fell by roughly 4x to 39x.

One headline result is the Reed–Solomon decoder used in decoded quantum interferometry (DQI), a leading candidate quantum optimization algorithm. Claude switched from the extended Euclidean algorithm to Berlekamp–Massey decoding and cut the decoder’s gate count about 12x compared with Google’s previous construction, from roughly 5.1 million Toffoli gates to about 440,000.

In the eighth task, elliptic-curve point addition, Claude found a new reversible way to perform modular inversion, which Anthropic calls the most expensive step in elliptic-curve calculations. The design makes a classical method called divsteps practical for quantum circuits. Anthropic says it came from a single 53-hour run with minimal human input, and that one circuit in the resulting family uses 12% more qubits but 17x fewer gates than the smallest previous design. Claude also formalized a key claim in the Lean proof assistant.

Caveats

Anthropic notes that Claude was conservative early on, so the setup required it to develop several different approaches in parallel, and researchers occasionally prompted it to think more broadly. Circuit design is also only one piece of a useful quantum computer: error correction, decoders and the hardware itself all still matter. Anthropic says the improvements could help practical quantum computers arrive sooner than previously anticipated.